Juncus arcticus (Baltic Rush)

Plant Info
Also known as: Mountain Rush
Genus:Juncus
Family:Juncaceae (Rush)
Life cycle:perennial
Origin:native
Habitat:sun; moist to wet; shores, ditches, wet meadows, marshes, fens
Fruiting season:June - July
Plant height:8 to 40 inches
Wetland Indicator Status:GP: FACW MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 6-petals Cluster type: panicle

[photo of primary bracts] Branching cluster at the top of the stem, the branches ascending to spreading with 6 to many flowers, the cluster compact or open and loose. The cluster is subtended by an erect bract that is round in cross-section and appears to be a continuation of the stem, with the cluster erupting from the side of the stem. The bract is several times longer than the cluster and up to 1/3 as long as the stem.

[photo of flowers] Flowers are single, not in heads of 2 or more, on stalks of varying lengths, with 6 tepals (petals and similar sepals) in 2 layers, 3.5 to 5.5 mm long, the inner and outer tepals about equal in size and shape, sharply pointed at the tip. Tepals are green along the midrib with a dark purplish brown to tan stripe along either side and translucent, white papery edging. Flowers have a 3-parted pink style and 6 yellow stamens, the anthers (tips) much longer than the filament (stalk).

Leaves and stems: Leaf attachment: basal Leaf type: simple

[photo of basal sheaths] A flowering stem has no leaves to speak of, just one to several bladeless sheaths at the base. Sheaths are reddish at the base and green to brown above. Stems are dark green, round in cross-section, smooth, erect, unbranched, and create colonies from long rhizomes.

[photo of stems arising in lines] Stems typically arise at regular intervals and in straight lines along the rhizome, most easily seen in sandy habitats where competition is reduced.

Fruit: Fruit type: capsule/pod

[photo of mature fruit] The tepals persist and become dark brown and appressed to erect in fruit. Fruit is an oval, 3-chambered capsule 3.5 to 4.5 mm long, reddish brown when mature, as long as or slightly longer than the tepals, rounded at the tip with a short beak at the top. Inside the capsule are numerous tiny seeds, .6 to .8mm long, dark amber to brown when mature, elliptic, somewhat flattened on the ends and no elongated tails.

Notes:

Across its range, Juncus arcticus is commonly found on sandy beaches but in Minnesota we most often encountered it in road ditches where the dark green stems look almost black against the lighter green of surrounding vegetation. The straight line growth and often dark purplish-brown tepals may also be distinguishing but the color can be variable and the lines are not as distinct when mixed with other vegetation, as in a road ditch. There are 3 Juncus species in Minnesota that have a lateral cluster with the bract appearing to be a continuation of the stem. Of the other two, Juncus effusus typically has more numerous flowers and forms dense clumps, Juncus filiformis typically has fewer flowers and a nearly round capsule, and its bract is much longer, often longer than the stem. The taxonomy for some Juncus species is a bit confusing, including this one. Minnesota currently follows Flora of North America, which calls the species found here Juncus arcticus subsp. balticus, where other references may call it Juncus balticus subsp. littoralis or Juncus arcticus subsp. littoralis. The DNR currently is undecided as to its native status in the state, though the consensus elsewhere is it's native and we're inclined to agree. Suffice to say more research is needed to clear the fog and straighten it all out.

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More photos

Photos by K. Chayka taken in Becker and Roseau counties. Photos courtesy Peter M. Dziuk taken in Kittson, Marshall and Otter Tail counties.

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